Abstract: To better understand the responses after antibiotic treatment in the 2017-2019 MWG, to contrast the metabolic outcomes achieved by HFD- and Westernized-diet feeding, and to address practical considerations, institutional limitations, and expected results for MMPC clients looking to implement FMT, we propose in Aim 1 to comprehensively characterize the molecular impact of antibiotic treatment on intestinal inflammation and bile acid metabolism; in Aim 2 to determine the effect of antibiotic treatment on expression of metabolic phenotypes in mice maintained on a Westernized high fat, high sugar diet; and in Aim 3 to determine the efficacy of FMT into germ-free mice as a tool for assessing the contribution of microbiota in (A) conferring protection or (B) conferring susceptibility to obesity and related comorbidities. Completion of these Aims, of interest to the NIDDK, will further the MMPC mission by providing data that will increase the rigor and reproducibility of investigator-initiated research studies.